A known method for treating intervertebral disc defects is removal by operation of the defective intervertebral disc and stiffening the intervertebral disc space with two vertebral bodies or, after removal of the defective intervertebral disc, subsequent insertion of an artificial intervertebral disc. In the first case, the sections of the vertebral column adjacent to the stiffened section are unnaturally stressed and, in the second case, simulation of the properties of a natural intervertebral disc is still unsatisfactory.
EP 0 669 109 B1 describes a device for stabilizing adjacent thoracic vertebrae, with which a damaged intervertebral disc and the intervertebral joints can be partly relieved from stress posteriorly. The device has two pedicle screws, which are rigidly connected in each case to a band consisting of an elastic synthetic material and are connected to one another via the biased band. To transmit pressure forces, a compression-proof body pushed on to the elastic band is further provided between the two screw heads. The use of a band of this kind does not however produce any guidance stability of the movement segment of a vertebral column. Nor is it possible to adjust the adjacent vertebrae in their positioning relative to one another, because the force transmission behaviour of the band and the pressure element via the bone screws is non-specific.
EP 0 518 567 B1 describes a device for stabilizing adjacent vertebrae, which has a damping element consisting of an elastomer, which is provided between two monoaxial screws screwed into the vertebrae. Each end of the damping element is connected a spherical head of the bone screw, which can be inserted into a receiving part of the bone screw and fixed therein. Thus, a minimal adjustment of the angle of the bone screw relative to the longitudinal axis of the damping element is possible. However, for each pair of vertebrae to be connected to one another an individually matching damping element with exact length and exact cross-section has to be made. Furthermore, the force transmission behaviour of the damping element is undefined, as it yields not only to axial, but also to bending and torsional forces.
It is further known to provide for fixing the vertebral column or sections of the vertebral column with an implant system consisting of a rod and at least two pedicle screws rigidly connected to the rod and screwed into corresponding vertebrae. However, with this implant system it is not possible to provide for dynamic movement control of the intervertebral disc or for dynamic takeover of stress to relieve the stress on a intervertebral disc.
U.S. Pat. No. 5,672,175 describes a dynamic implanted spinal orthosis which attempts to preserve at least in part the natural mobility of the vertebrae while effecting and maintaining a correction of the relative positions of the vertebrae without osteosynthesis, graft or fusion. As such, anchoring components are fixed to the vertebrae, each anchoring component comprising at least one plate having an anterior convex face coming to bear in contact with the vertebral lamina on at least one side of the spinous process. Cylinders of the coupling means are carried by a plate opposite the transverse end of the lamina near the transverse process. Each plate is fixed to a vertebrae on at least two different places, for example, by an intrapedicular screw and/or clamping hooks. Holding means are coupled to the plates, the holding means comprising an elastic return device for exerting forces for holding the vertebrae in the corrected position against natural deforming forces, thus treating a deformation of the spine.
U.S. Pat. No. 5,733,284 describes a device for anchoring rachidian instrumentation on a vertebrae. The device has structure very similar to the device described in U.S. Pat. No. 5,672,175.
It is still desirable to provide new and better dynamically acting stabilization devices for bones, in particular for adjacent vertebrae, with which it is possible both to position the bones or vertebrae and intervertebral joints in respect of one another and simultaneously, in a defined way, to support and partially relieve the stress on the intervertebral disc and intervertebral joints connected in between with respect to the forces to be transmitted.